wick et al., 1983). Living plants do not actively release high amounts of ITCs (Bö rner, 1961), because glucosi-The allelopathic potential of isothiocyanates (ITC) released by nolates are located in the vacuole and myrosinase is turnip-rape mulch [Brassica rapa (Rapifera Group)-Brassica napus L.] was evaluated. Six different ITCs were identified from chopped bound to the cell wall (Bjö rkman, 1976). As long as this turnip-rape by HPLC-DAD/HPLC-MS. All plant parts contained separation exists, there is only a low ITC content in the 2-phenylethyl-ITC. In the shoot n-butyl and 3-butenyl-ITC domicells (Tang, 1971). Larger amounts of ITCs can only nated. Younger leaves, flowers, and buds also contained small amounts be released by the breakdown of the cells, e.g., during of benzyl and allyl-ITC. Furthermore, marginal amounts of 4-pendecomposition of dead plant material (Bell and Muller, tenyl-ITC were detected. In the soil, where turnip-rape mulch was 1973), or even faster by incorporating green plant mateincorporated, only low amounts of ITCs were detected. It was shown rial into the soil. If Brassica spp. plant tissues are incorthat the DT 50 of ITCs in soil are very short. Germination tests with porated into the soil, it is possible to control weeds in weed seeds in aqueous ITC solutions showed, that aryl-ITCs were the following crop by ITCs released from the mulch the most suppressive compounds. Within the alkyl-ITCs, the activity decreased with increasing molecular mass. The susceptibility of differ- (Brown and Morra, 1995; Boydston and Hang, 1995; ent weed species to ITCs mainly depended on seed size. Smaller seeds Al-Katib et al., 1997). This might be a chance to reduce tended to be more sensitive. Further studies demonstrated a high the use of herbicides and could be an additional tool to biological activity of ITCs in the vapor phase. n-Butyl-ITC was more control herbicide-resistant weeds. suppressive in the vapor phase than in aqueous solution, while 2-The objectives of this study were to evaluate the allelphenylethyl-ITC showed the opposite effect. Results demonstrated opathic potential of ITCs released by turnip-rape that weed suppression observed in the field was probably due to the mulch. Therefore, the content of ITCs in different parts high amounts of ITCs identified in turnip-rape mulch. Isothiocyanates of turnip-rape, and in the soil after incorporation was were strong suppressants of germination on tested species-spiny determined, and the phytotoxicity of different ITCs on sowthistle [Sonchus asper (L.) Hill], scentless mayweed (Matricaria inodora L.), smooth pigweed (Amaranthus hybridus L.), barn-several weed species-spiny sowthistle [Sonchus asper yardgrass [Echinochloa crusgalli (L.) Beauv.], blackgrass (Alopec-(L.) Hill], scentless mayweed (Matricaria inodora L.), urus myosuroides Huds.), and wheat (Triticum aestivum L.)-and smooth pigweed (Amaranthus hybridus L.), barnprobably interact with weed seeds in the soil solution and as vapor yardgrass [Echinochloa crusgalli (L.) Beauv.], blackin so...
Benzoxazinoids (Bx) are natural phytotoxins that function as chemical defense compounds in several species. The release of Bx by intact plant roots associated these compounds with root allelopathy in Triticeae species; however, the significance of exudate concentrations of Bx for plant-plant interactions is still a controversial question. A biological screening of 146 cultivars of four Triticeae species (Triticum aestivum L., Triticum durum Desf., Triticum spelta L., and Secale cereale L.) demonstrated a high cultivar dependence to suppress the root growth of Sinapis alba L. by root allelopathy in a dose-response bioassay. Only a few cultivars possessed a marked high or low allelopathic activity, whereby high-performance liquid chromatography-diode array detection analysis of root exudates revealed that these cultivars differed considerably in their ability to exude the two Bx aglucones, DIBOA [2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one] and DIMBOA [2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one]. The total amount of DIBOA and DIMBOA exuded showed a significant correlation to the growth inhibition in bioassay with a statistically estimated contribution to the overall allelopathic effect of 48-72%. In a bioassay with pure phytotoxins, Bx concentrations consistent with the amounts quantified in the screening bioassay caused detrimental effects on S. alba and almost reproduced the statistically estimated contribution. The observed causal association between the allelopathic activity under laboratory conditions and the exudate concentrations of Bx suggests that this association might have implications for the interference of Triticeae species in natural plant communities.
A biotype of Amaranthus retro¯exus L. is the ®rst weed in Israel to develop resistance to acetolactate synthase (ALS)-inhibiting herbicides. The resistant biotype (Su-R) was collected from Ganot, a site that had been treated for more than 3 consecutive years with sulfometuronmethyl + simazine. On the whole-plant basis, the resistance ratio (ED 50 Su-R)/(ED 50 Su-S) was 6±127 for sulfonylureas, 4±63 for imidazolinones, 20±35 for triazolopyrimidines and 11 for pyrithiobac-sodium. Similar levels of resistance were found also when the herbicides were applied before emergence. Based on a root elongation bioassay, Su-R was 3240-fold more resistant to sulfometuron-methyl than Su-S. In vitro studies have shown that the Su-R biotype was resistant at the enzyme level to all ALS inhibitors tested. The nucleotide sequences of two ampli®ed regions between the Su-S and the Su-R diered in only one nucleotide. One substitution has occurred in domain A, cytosine by thymine (CCC to CTC) at position 248, that confers an exchange of the amino acid proline in the susceptible to leucine in the Su-R 1. The proline to leucine change in domain A is the only dierence in the amino acid primary structure of the regions sequenced, indicating that it is responsible for the ALS-inhibitor resistance observed.
Apart from its competitive ability, the invasiveness of the noxious weed Parthenium hysterophorus L. is thought to be due to an ability to displace other species by means of allelopathy. The sesquiterpene lactone parthenin that is biosynthesized by this species is thought to play a role in its allelopathic interference with surrounding plants. However, despite the fact that parthenin is released from various plant parts into the soil, little is known about its relative contribution to overall allelopathic effects. Because leaf residues are believed to deliver large amounts of parthenin to soils during decomposition, we parthenin within leaf extracts were determined using HPLC, and the phytotoxicity of quantified extract concentrations was assessed in pure compound dose-response bioassays. A. conyzoides was again most sensitive, with ED 50 -values for inhibition of root length and germination by parthenin of 51.8 and 289.9 μg/ml, respectively. Furthermore, parthenin treatments proved to significantly delay germination and stimulate root growth at low doses. The contribution of parthenin to observed effects of leaf extracts was finally estimated by model comparisons of dose-response relations of parthenin in leaf extracts or as a pure compound. Results showed that the contribution of parthenin was highly dependent on its concentration within extract solutions and varied between 16% and 100% of overall phytotoxicity of leaf extracts. The inhibition could be completely reproduced by pure parthenin treatments in quantified amounts, when extract solutions with high levels of parthenin were tested on the most sensitive species, A. conyzoides.This suggested that the release of parthenin during decomposition of leaf material has a potential to play a leading role for allelopathy in P. hysterophorus; however, its significance in a natural setting will very much rely on the amount of leaf material accumulated on soil surfaces and the concentration of parthenin in residues.
The response of an organism to a chemical depends, among other things, on the dose. Nonlinear dose-response relationships occur across a broad range of research fields, and are a well established tool to describe the basic mechanisms of phytotoxicity. The responses of plants to allelochemicals as biosynthesized phytotoxins, relate as well to nonlinearity and, thus, allelopathic effects can be adequately quantified by nonlinear mathematical modeling. The current paper applies the concept of nonlinearity to assorted aspects of allelopathy within several bioassays and reveals their analysis by nonlinear regression models. Procedures for a valid comparison of effective doses between different allelopathic interactions are presented for both, inhibitory and stimulatory effects. The dose-response applications measure and compare the responses produced by pure allelochemicals [scopoletin (7-hydroxy-6-methoxy-2H-1-benzopyran-2-one); DIBOA (2,4-dihydroxy-2H-1,4-benzoxaxin-3(4H)-one); BOA (benzoxazolin-2(3H)-one); MBOA (6-methoxy-benzoxazolin-2(3H)-one)], involved in allelopathy of grain crops, to demonstrate how some general principles of dose responses also relate to allelopathy. Hereupon, dose-response applications with living donor plants demonstrate the validity of these principles for density-dependent phytotoxicity of allelochemicals produced and released by living plants (Avena sativa L., Secale cereale L., Triticum L. spp.), and reveal the use of such experiments for initial considerations about basic principles of allelopathy. Results confirm that nonlinearity applies to allelopathy, and the study of allelopathic effects in dose-response experiments allows for new and challenging insights into allelopathic interactions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.